Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
  • G01F1/7044—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter using thermal tracers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
  • G01F1/708—Measuring the time taken to traverse a fixed distance
  • G01F1/7086—Measuring the time taken to traverse a fixed distance using optical detecting arrangements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
  • G01P5/18—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance
  • G01P5/22—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance using auto-correlation or cross-correlation detection means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
  • G01F1/708—Measuring the time taken to traverse a fixed distance
  • G01F1/712—Measuring the time taken to traverse a fixed distance using auto-correlation or cross-correlation detection means

Definitions

• the invention relates to a method for measuring a flow rate of a gas flow.
• the invention relates to a device for measuring a flow velocity of a gas stream, with (a) a first IR radiation sensor for time-resolved measurement of a first IR radiation parameter of IR radiation of the gas stream in order to obtain an IR radiation parameter profile, (b) a second IR radiation sensor for measuring a second IR radiation parameter of IR radiation of the gas stream to obtain a second IR radiation parameter profile, and (c) an evaluation unit which is designed to automatically calculate a transit time between the first IR radiation pair - the course of the parameters and the second course of the IR radiation parameters, in particular by means of cross-correlation, and calculating the flow velocity from the transit time.
• the flow velocity of gases has to be measured in many places. This measurement task is particularly challenging when the gases are very hot and / or aggressive. At high temperatures, for example above
• temperature-resistant materials must be used, which is complex. Aggressive gases lead to increased wear. If the gas flow carries, for example, solid particles, for example ash, coal, slag or cement particles, there may be significant abrasive wear on the measuring device used. If the gas contains oxidizing components, for example, chemical wear can also occur. In spite of possibly adverse environmental conditions, a high level of measurement accuracy is desirable because, for example, this improves the controllability of the technical system on which the flow velocity is measured. It is known to measure temperature fluctuations in the gas stream at locations spaced apart from one another and to determine the temporal offset of the two temperature profiles by means of cross-correlation. The flow velocity of the gas flow can be determined from the time offset and the distance between the measuring points.
• DE 38 27 913 A1 discloses a method and a device for determining the speed of a flow, in which scattered light measurements are carried out on parts. The respective measuring locations are spaced apart. The speed is obtained from a correlation calculation on the measurement results.
• a method for measuring the gas flow is known from US Pat. No. 9,157,778 B2, in which the absorption of radiation is measured at two measuring locations spaced apart from one another.
• the flow rate is calculated by determining the running time of a disturbance. This disturbance can be caused, for example, by the initiation of gas.
• the object of the invention is to improve the measurement of the flow velocity of a gas stream.
• the invention solves the problem by a method with the steps (a) time-resolved measurement of an IR radiation parameter of IR radiation of the gas stream at a first measuring point outside the gas stream, so that a first IR radiation parameter course is obtained, (b) time-resolved measurement of the IR radiation parameter at a second measuring point outside the line, so that a second IR radiation parameter course is obtained, (c) calculation of a transit time from the first IR radiation parameter course and the second IR Radiation parameter curve, in particular by means of cross correlation, and (d) calculating the flow velocity from the transit time, with (e) the IR radiation parameter being measured photoelectrically at a wavelength of at least 780 nm, in particular 1.5 miti.
• the invention solves the problem by a generic device in which the IR radiation sensors are photoelectric IR radiation sensors and have a measuring range, the lower limit of which is at least 0.78 pm and a measuring frequency of have at least 1 kilohertz.
• An advantage of the invention is that the flow speed can be measured with a higher accuracy.
• the reason for this is that the photoelectric measurement of the IR radiation parameter is absolutely possible, which is usually only possible with a pyrometric measurement, for example, if the emission coefficient is constant, which often cannot be guaranteed.
• the IR radiation parameter is measured at a wavelength of at least 0.78 pm, in particular at least 1.5 pm.
• Blackbody radiation can originate, for example, from the walls of a line which carries the gas stream or from particles in the gas stream. Gases with excitation wavelengths above 1.5 pm absorb and re-emit in the wavelength range, the background blackbody radiation, so that fluctuations in the gas concentrations are particularly pronounced.
• the time-constant background is irrelevant, for example, when calculating using cross correlation.
• the IR radiation parameter is measured at a wavelength of at most 6 pm, in particular at most 5.3 pm. It has been shown that a particularly high measurement accuracy for the flow velocity can be achieved in this way.
• the invention is based on the knowledge that local fluctuations or inhomogeneities in the IR radiation parameter are similar for such a long time that these fluctuations move at the same speed as the gas stream itself. These fluctuations can have several causes. On the one hand, there can be thermal fluctuations, which means that the temperature of the gas flow is spatially inhomogeneous at a given point in time. If this inhomogeneity moves with the flow rate of the gas stream, the flow rate can be inferred from the temperature fluctuations.
• the gas is a mixture of different gases, ie if the gas is a gas mixture as provided in a preferred embodiment, there may be fluctuations in the concentration of the gases.
• the spatial distribution of the gas concentration has proven to be more locally stable than the temperature distribution. The reason for this could be that three mechanisms for compensating for temperature differences are known, namely mixing, heat conduction and heat radiation. In contrast, fluctuations in concentration can only be compensated for by diffusion. The local distribution of concentration differences is therefore more stable over time. For this reason, the first IR radiation parameter curve and the second IR radiation parameter curve are more similar to one another, so that the calculation of the transit time is possible with less measurement uncertainty.
• the IR radiation parameter is understood to mean a value or a vector which specifies the irradiance of the electromagnetic infrared radiation which is caused by the IR radiation of the gas stream in a measurement interval. If the density, the temperature and the composition of the gas flow change, the IR radiation parameter also changes.
• the gas stream preferably flows in a line and the IR radiation parameter is measured from a measuring location outside the line.
• the gas flow spreads freely, for example flows out of an outflow opening and escapes into the environment or a larger cavity.
• the measurement frequency is preferably at least 1.5 kilohertz, particularly preferably at least 16 kilohertz.
• the higher the measurement frequency the lower the measurement uncertainty with which the runtime is determined.
• the radiation parameter is preferably measured analogously, but then digitized, the bit depth preferably being 16 bits.
• the gas stream is a stream of a gas mixture which contains a first gas and at least a second gas, the first gas having a first gas excitation wavelength and the IR radiation parameter being an irradiance of an IR radiation sensor
• First gas excitation wavelength is.
• the first gas can be, for example, water vapor, nitrous oxide, methane, carbon dioxide, carbon monoxide, sulfur dioxide or sulfur trioxide, NOx, H2S, HF, NH3 and all IR-active molecules.
• the second gas is a different gas than the first gas and also, for example, water vapor, nitrous oxide, methane, carbon dioxide, carbon monoxide, sulfur dioxide or sulfur trioxide.
• the IR radiation parameter is an irradiance at the first gas excitation wavelength is understood in particular to mean that a change in the concentration of the first gas under otherwise identical conditions leads to a change in the IR radiation parameter.
• Radiation components that lie outside a predetermined measurement interval that contains the first gas excitation wavelength are preferably filtered out.
• the interval width of this measurement interval is preferably less than 0.5 ⁇ m, preferably less than 0.4 pm.
• the second gas preferably has a second gas excitation wavelength and the method comprises the steps (a) time-dependent detection of a second IR radiation parameter in the form of an irradiance at the second gas excitation wavelength at the first measuring point, so that a first irradiance curve is obtained , (b) time-dependent detection of the second IR radiation parameter at the second measuring point so that a second irradiance curve is obtained, (c) calculating a second transit time between the irradiance curves, in particular by means of cross-correlation, and (d) calculating the Flow rate from the first runtime and the second runtime.
• the transit times are measured using two different concentration fluctuations. This has the advantage that the measurement uncertainty can be further reduced.
• IR radiation of the gas stream which is not within a predetermined measuring interval of, for example, ⁇ 0.3 pm around the first gas excitation wavelength or within a predetermined interval of ⁇ 0.3 pm around the second gas excitation wavelength is preferred , filtered out. It is particularly preferred to filter out IR radiation that does not lie in predetermined intervals of ⁇ 0.2 pm around the respective excitation wavelength. The advantage of this is that the measurement uncertainty can be reduced further, because there are fewer overlaps with other fluctuating radiation components, which can lead to an averaging effect.
• a temperature of the gas stream is preferably at least 200 ° C., particularly preferably at least 1000 ° C. The advantages of the invention are particularly evident at high temperatures.
• An indium arsenic antimony detector is preferably used to measure the IR radiation parameter.
• a mercury-cadmium tellurite detector can be used.
• the measuring range of the IR radiation sensors is preferably between 1 and 6 pm, in particular between 1, 5 and 6 pm. It is advantageous if the evaluation unit is set up to automatically carry out a method according to the invention. This is to be understood to mean that the evaluation unit carries out the method automatically without human intervention.
• the device prefferably has a line for guiding the gas flow, the first IR radiation sensor and the second IR radiation sensor for detecting IR radiation being arranged outside the line.
• the IR radiation sensors are arranged outside the line. If the temperature of the gas flow during operation of the device is greater than 200 ° C., the IR radiation sensors are preferably arranged so far from the gas flow that the temperature there is at most 100 ° C., preferably at most 80 ° C.
• the spacing of the IR radiation sensors from the gas flow also has the advantage that the chemical and / or abrasion wear can be negligibly small.
• the device (a) according to the invention preferably has a first measuring line which runs transversely to the line of the gas stream and which is designed to conduct a first bundle of IR radiation from the gas stream to the first IR radiation sensor,
• a second measuring line which runs transversely to the line and which is designed to conduct a second IR radiation beam from the gas stream to the second IR radiation sensor, the measuring lines being arranged in such a way that the IR radiation beams have a misalignment angle f of at most 45 °, in particular at most at most 20 °, preferably at most 10 °, with one another.
• the turbulence patterns at the first measuring point and at the second measuring point are particularly similar, so that a small measurement uncertainty of the flow rate can be achieved.
• the IR radiation sensors are preferably not sensitive below a wavelength of 1.5 miti, preferably below 780 nm. This means that the spectral sensitivity below this wavelength is at most a third in particular at most one tenth, which is the maximum spectral sensitivity.
• the spectral sensitivity is given, for example, in amperes per watt.
• the IR radiation sensors are also preferably no longer sensitive above 15 miti, preferably above 5.5 miti.
• the wavelength interval between 1, 5 and 6 miti are vibration excitation wavelengths of frequently occurring gases, such as carbon dioxide, carbon monoxide and water.
• the blackbody background radiation is sufficiently intense to obtain a good signal-to-noise ratio.
• the IR radiation sensors are preferably arranged such that a maximum diameter of the IR radiation beam is at most 200 millimeters.
• the first IR radiation sensor is arranged such that the first IR radiation beam runs in a first straight line
• the second IR radiation sensor is arranged such that the second IR radiation beam runs along a second straight line and that a distance of minimum distance between the two straight lines extends in the direction of flow.
• the distance between the two straight lines is the measuring distance.
• the measuring distance is preferably at least 50 to 1000 millimeters, in particular at most 600. It is also expedient if the measuring distance is at most 600 millimeters.
• the measurement distance between the two straight lines preferably corresponds at least to the quotient of the flow rate and 1000 Hertz and / or at most the quotient of the flow rate and 100 Hertz. At this distance, the measurement uncertainty when determining the flow rate is already very low due to the uncertainty in the running time. In addition, the uncertainty caused by a change in the inhomogeneity pattern is not yet too great to have a negative impact on the measurement uncertainty.
• the device preferably does not protrude into the line. This is to be understood in particular to mean that no part of the device protrudes more than a tenth into the cross section of the line.
• Prior art systems often have lances that create turbulence in the gas stream. The disadvantage of this is that this leads to a loss in flow velocity and thus to a loss in the efficiency of the monitored system.
• the IR radiation parameters are preferably measured on an undisturbed or not actively disturbed gas stream.
• FIG. 1 shows a device according to the invention for carrying out a method according to the invention according to a first embodiment
• Figure 2 shows an inventive device for performing an inventive method according to a second embodiment.
• FIG. 3 shows a device according to the invention for carrying out a method according to the invention in accordance with a third embodiment.
• FIG. 1 shows a combustion system 10 in which a gas stream 14, in the present case in the form of an exhaust gas stream, is generated by combustion or other exothermic processes or external heat supply of a fuel by means of a burner 12.
• the firing system 10 can, as in the present case, be a device for heating a metal bath or glass bath 16. However, the furnace can also be part of a power plant or cement plant, for example. A furnace, power plant or cement plant with a measuring device according to the invention is also an object of the present invention.
• the gas stream 14 runs through a line 18.
• FIG. 1 also shows a measuring device 20 for measuring a flow rate vG of the gas stream 14.
• the flow rate vG is the average flow rate which, by multiplying by a cross-sectional area A of the line 18, gives the volume flow of gas.
• the line 18 is circular, so that the cross-sectional area increases
• the measuring device 20 comprises an IR radiation sensor 22.1 and a second IR radiation sensor 22.2.
• the first IR radiation sensor 22 is arranged to detect a first IR radiation beam 24.1, which propagates through a measuring line 25.1.
• a schematically shown molecule 26.1 which is located in the first IR radiation bundle 24.1, emits an IR photon 28, which moves in the first IR radiation bundle 24.1 towards the first IR radiation sensor 22.1, then this strikes a sensor sorelement 30.1 in the form of an InAsSb photo detector, which then generates a voltage.
• the photo voltage Ui generated by the sensor element 30.1 thus depends on the irradiance of the radiation that falls on the sensor element 30.1.
• the sensor element 30.1 is arranged at a distance from the line 18.
• the measuring line 25.1 does not protrude into the line 18, so that the formation of additional turbulence is largely excluded.
• the raw analog data is converted into digital values by an analog-digital converter of the radiation sensor 22.1.
• the bit depth of the scan is 8 to 24, preferably 16 bits.
• the second IR radiation sensor 22.2 is designed to measure radiation from an IR radiation beam 24.2, which propagates in a second measuring line 25.2.
• the IR radiation of the second IR radiation beam 24.2 comes, for example, from a second molecule 26.2.
• the first IR radiation beam 24.1 extends along a first straight line G1
• the second IR radiation beam 24.2 extends along a second straight line G2.
• the two straight lines G1, G2 have a measuring distance d from each other. As shown in the present case, they preferably run parallel to one another.
• the measuring distance d is preferably at most 500 millimeters, for example 350 ⁇ 50 millimeters.
• the photo voltages Ui, U2, which are generated by respective sensor elements 30.1, 30.2, are sent to an evaluation unit 32.
• the photo voltage Ui is a measure of an irradiance Ei, which the sensor element 30.1. is measured and represents an IR radiation parameter.
• the irradiance E2 is measured by the second sensor element 30.2 and is also time-dependent.
• a local concentration c of a first gas g1 fluctuates in the exhaust gas stream 14, for example methane, water, carbon dioxide, carbon monoxide, sulfur trioxide, sulfur field dioxide or nitrous oxide
• Blackbody radiation emanating from a wall 34 in line 18 does not interfere with this measurement.
• H2O is selected as the first gas
• this has a first gas excitation wavelength l 9 i of 3.2 pm.
• a second gas g2 is selected, the second gas excitation wavelength l 9 2 of which is not in the measurement interval M for the first gas g1, the measurement accuracy can often be increased.
• FIG. 2 schematically shows a jet engine 36 on which the measuring device 20 is arranged such that the gas stream 14, which in this case exits the jet engine 36 through an outflow opening 38, is measured.
• FIG. 3 schematically shows part of an arc furnace 40 with a melting vessel 42 in which steel scrap is melted by means of an arc between electrodes 43.1, 43.2, 43.3, so that the metal bath 16 is formed.
• a melting vessel 42 in which steel scrap is melted by means of an arc between electrodes 43.1, 43.2, 43.3, so that the metal bath 16 is formed.
• Exhaust gases formed in the melt form the gas stream 14 and are discharged through the line 18.
• the line 18 has an annular gap 44 through which air 46 can additionally enter the line 18.
• the measuring device 20 is arranged on the gap 18 on the line 18.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Measuring Volume Flow (AREA)

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Citations (9)

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• 2018
  • 2018-09-24 DE DE102018123448.1A patent/DE102018123448A1/de active Pending
• 2019
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  • 2019-09-24 ES ES19779430T patent/ES2966165T3/es active Active
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  • 2019-09-24 EP EP19779430.8A patent/EP3857177B1/de active Active
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